1. Field of the Invention
The present invention relates to multiconductor, multifilar coils utilized in a pacing lead assembly.
2. Description of the Prior Art
Heretofore multifilar, single conductor coiled pacing leads have been utilized in pacing lead assemblies having a multipolar electrode assembly at the distal end thereof and a connector at the proximal end thereof for connecting the conductor lead to a pulse generator. An example of such a bipolar lead assembly is disclosed in U.S. Pat. No. 4,236,525 which discloses a lead assembly for a body implantable tissue stimulator having two distal electrodes and proximal connectors that are coaxially and axially spaced for mating with corresponding stimulator output electrodes in a pulse generator.
The connectors heretofore utilized for connecting the proximal end of a multifilar conductor pacing lead to a pulse generator such as the connectors disclosed in U.S. Pat. No. 4,236,525 have worked satisfactorily. However, due to recent developments in cardiac pacing technology, leads having multiple conductors but of the same diameter or a small diameter than unipolar and bipolar leads are necessary.
The insert connector at the proximal end of the pacing lead of the present invention solves this problem by providing one or more spool-shaped metal bands about the proximal end of the pacing lead and connected to individual wire conductors of the lead with an elastic conductive ring positioned about the spool adapted to contact a metal sleeve or ring embedded in the side wall of a socket in a body portion of the pulse generator into which the insert connector is inserted.
Also as will be described in greater detail hereinafter, the multipolar electrode assembly at the distal end of the multiconductor pacing lead of the present invention is constructed in such a way as to facilitate solid electrical contact between the ends of each wire conductor in the multiconductor lead and individual electrodes of the electrode assembly and in such a way as to take up a minimum of space thereby to enable a very compact minimum diameter electrode assembly to be provided.
In the forming of a multiconductor lead, a plurality, such as three, insulated wire conductors are wound on a wire mandrel so as to form a multi-conductor coiled lead having the outside diameter of only one coil, i.e., the diameter of the winding mandrel plus twice the diameter of the insulated coated wire. However, this technique for making such a minimum diameter multiconductor coil has not provided a coil wherein the insulating coating is homogenous throughout the multiconductor coil. In this respect, due to the tension which has to be applied to the coated wires in attempting to wind them on the winding mandrel, the wire may act like a "cheese cutter" and cut through the part of the insulating coating which is between the wire and the winding mandrel. When this happens, the inside surfaces of the coiled wires are no longer insulated, the enclosing envelope of insulation around the wires is no longer intact and the insulating materials can part company from the wire allowing them to touch and short circuit. Also, a short circuit could be formed when a wire stylet is inserted within the enclosing envelope and makes contact with the exposed wires.
An example of the prior art technique for winding one or more insulated wire conductors on a mandrel is disclosed in U.S. Pat. No. 3,572,344.
As will be disclosed in greater detail hereinafter, the method of the present invention eliminates this problem of breaks in the insulating coating by forming the individual wire coils that are to be combined in a multiwire conductor coil in an uninsulated form on a winding mandrel. Then, the uninsulated wire conductor coils thus formed are coated with an insulating material and the coated wire conductor coils are screwed into one another thereby to form a multiconductor coil.